Wavelength stabilized, tunable optical transmitter with high SMSR

Abstract

In practical WDM systems, the maximum SMSR for each channel does not necessarily occur where dPout / dItune=0. In fact, for most channels the maximum SMSR occurs at values of tuning current where this first derivative in not zero. In accordance with one aspect of the invention, a wavelength stabilized optical transmitter includes a DBR laser and a feedback loop for controlling the center wavelength of the laser, characterized in that the transmitter also includes a memory in which are stored the non-zero values of dPout / dItune where the SMSR is a maximum for each of a multiplicity of different channel wavelengths and further includes a controller responsive to the stored values for delivering to the laser a level of tuning current that maximizes the SMSR for a particular channel wavelength.

Description

This invention relates generally to tunable optical transmitters, and, more particularly to such transmitters that include tunable DBR semiconductor lasers and arrangements for stabilizing such lasers and for maintaining their side mode suppression ratio (SMSR) relatively highWavelength division multiplexed (WDM) optical networks increase the information carrying capacity of a communication (e.g., transmission) system by loading multiple channels, each at a different carrier frequency or wavelength, onto a single optical fiber. Over the last few years, the channel density of commercial WDM systems has increased dramatically. At the present time, for example, commercially available systems are available that operate at carrier wavelengths around 1.55 .mu.m and that carry 80 individual channels spaced at 50 GHz. Even larger capacity systems are being planned. These systems are often referred to as dense WDM or DWDM systems. It is advantageous in such systems to use optical sources (or...

AI Technical Summary

Benefits of technology

In practical WDM systems, I have found that the maximum SMSR for each channel does not necessarily occur where dP.sub.out / dI.sub.tune =0. In fact, in a representative case the SMSR at dP.sub.out / dI.sub.tune =0 may be 3-5 dB below the maximum; i.e., for most channels the maximum SMSR occurs at values of tuning current where this first derivative is not zero. Taking advantage of this discovery, in accordance with one aspect of the invention, a wavelength stabilized optical transmitter includes a DBR semiconductor laser and a feedback loop for controlling the center wavelength of the laser, characterized in that the transmitter also includes a memory in which are stored the non-zero values of dP.sub.out / dI.sub.tune where the SMSR is a maximum for each of a multiplicity of different channel wavelengths and further includes a controller responsive to the stored values for delivering to the laser a level of tuning current that maximizes the SMSR for a particular channel wavelength. dr

Problems solved by technology

However, as these systems are operated for long periods of time, the DBR semiconductor lasers tend to degrade in performance due to aging and material defects.

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